Papermaking method and apparatus



juiy 18, 1967 PAPERMAKING METHOD AND APPARATUS Filed June 21,. 1965 5 Sheets-Sheet 1 c. A. LEE 3,331,138

Jufly E8, 1967 c. A. LEE

PAPEHMAKING METHOD AND APPARATUS 3 Sheets-Sheet 2 Filed June 21. 1965 n WW 6444 45: 4446' 46s MA, #211, r 50 3.7%;

A rv-rs MW W w mm mm iggggghagi \M mm QR gm Juiy E8, 1967 c. A. LEE

PAPERMAKING METHOD AND APPARATUS 5 Sheets-Sheet Filed June 21. 1965 United States Patent 3,331,138 PAPERMAKING METHOD AND APPARATUS (Iharles Allen Lee, Knoxville, Tenn, assignor, by Inesne assignments, to International Paper Company, New York, N.Y., a corporation of New York Filed June 21, 1965, Ser. No. 465,688 13 Claims. (Cl. 3423) This invention relates generally to the art of papermaking, more particularly to the drying of a wet paper web, and still more particularly to ventilating the moistureladen pockets in the drier section of a papermaking machine each bounded by a drier fabric, the paper web and a drying cylinder.

Common papermaking machines conventionally include a drier section in which the paper web is trained around a number of heated drying cylinders for evaporating water from the paper. These cylinders are disposed in two parallel rows, one row above the other. The paper web is wrapped over the upper drying cylinders and under the lower drying cylinders to dry the paper from both sides, passing alternately over an upper cylinder and under a lower cylinder. The traveling web is urged against the drying cylinders by drier fabrics which have generally been of low permeability felts woven of cotton or other fibers. These drier fabrics are thus disposed on the side of the paper web away from the drying cylinders and are supported out of contact with the paper web as the web travels from one cylinder to the next. This results in the formation of open ended pockets each bounded by a drier fabric, the paper web and a drying cylinder. Moisture evaporated from the paper web by the drying cylinders accumulates in these pockets, particularly in the center thereof, and interferes with the efificient and uniform drying of the web.

The entrapment and accumulation of this moisture has often resulted in the paper being too dry in certain areas and too wet in others. A common way of reducing this problem is to blow air through the pockets from one end to the other. To avoid drying one edge of the paper more than the other, the air was blown in one direction through some pockets and in the opposite direction through other pockets. This still resulted in uneven drying. For example, in the case of newsprint, such drier sections of the prior art have produced paper of the desired 8 to 10 percent moisture in the center while drying the edges to 4 percent. Nonuniform drying generally produces an inferior paper product. It produces a paper of nonuniform strength because of the uneven contraction of the drying web on the driers occasioned by the difference in contraction at different moisture contents. Further, nonuniform moisture content results in nonuniform conditions of bulk, and when a web of nonuniform bulk is compressed in a breaker stack or calender stack of a papermaking machine, differences in finish are produced, resulting in nonuniform receptivity to coatings or ink. Nonuniformity in drying adds substantially to the cost of drying, for paper must ordinarily be dried until the wettest part of the web is dried below a certain maximum; this means that the other parts must be wastefully overdried at unnecessary and unproductive expense.

For a more uniform condition of dryness, it is known to force pressurized air through the drier fabric across the entire width of the fabric. This has required seals and sometimes pressurized porous rolls. The seals have required complex engineering and were inherently undesirable, for they added friction drag which both increased the power needed to drive the machine and wore out the drier fabrics. Where the seals were not tight, a substantial amount of the pressurized air was forced out through the seals without passing through the drier fabric.

Pressurized porous rolls have proven exceedingly expensive in both initial cost and in maintenance.

In accordance with the present invention, the pockets are ventilated with air driven through the drier fabric at low pressure, preferably subatmospheric, so that seals and porous rolls are unnecessary. To achieve this, there is provided an open-mesh dn'er fabric many times more air permeable than conventional drier felts, and the air is driven toward the fabric in the form of a jet at relatively high linear velocity, whereby the kinetic energy of the jet of air drives it through the drier fabric while at the same time reducing the static pressure of the air to near atmospheric pressure. Under such conditions substantially all of the air in the jet passes through the fabric into the pocket and relatively little is wasted. At subatmospheric pressures the jet will actually reduce additional air from the surrounding atmosphere and carry it through the fabric. The air, after being driven through the fabric, passes out the open ends of the pockets, carrying moisture out with it and thus purging the pocket of moisture. The jet is distributed in the cross machine direction so as to produce the desired moisture content along substantially the entire length of the pocket. Since it is desired to produce a uniform dryness in the web, it is often desirable to provide a uniform moisture content in the pocket across its entire length; however, the pocket ventilators are not necessarily used in every pocket, and it is therefore often desirable to compensate for nonuniformity of moisture distribution in a preceding or succeeding unventilated pocket by providing the distribution of air in a ventilated pocket that produces a complementary moisture distribution. The distribution of air may also compensate for other causes of nonuniformity in drying in order that the ultimate paper may have the desired uniformity. Further, the air jet is given a substantial component of velocity in the direction of the open ends to aid in purging the moistureladen air without requiring a great head of static pressure.

It is therefore a primary object of this invention to ventilate the pocket bounded by the drier fabric, the paper web and a drying cylinder 'to purge the moisture-laden air therefrom. It is a further object to provide a method and apparatus for achieving such ventilation by passing air through the drier fabric without using pressure seals at the fabric to confine the air. It is still another object of the present invention to utilize an air permeable drier fabric and jetting air at the fabric at sufiiciently high veloc ity that substantially all of it passes through the fabric into the pocket. A still further object is to provide such method and apparatus for developing a desired condition of humidity in the pocket across the machine.

Other objects and advantages of the invention will become apparent from the following description, particularly when taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a side elevation view of a portion of a typical drier section of a papermaking machine and includes pocket ventilating means in accordance with a preferred form of the present invention;

FIGURE 2 is an elevation view partly in section of the pocket ventilating means shown in FIGURE 1, taken along line 22 of FIGURE 1;

FIGURE 3 is a plan view of the apparatus shown in FIGURE 2, taken along line 3-3 of FIGURE 2 with the associated roll removed;

FIGURE 4 is an enlarged sectional view of the apparatus shown in FIGURE 2, taken along the 4-4 of FIGURE 2; and

FIGURE 5 is an enlarged view of one form of pocket ventilating means shown in FIGURE 1.

Referring to the drawings, FIGURE 1 shows the drier section of a papermaking machine including an upper row of drying cylinders 10, 12, 14, 16 and a lower row of drying cylinders 18, 20, 22, 24. These cylinders rotate in the direction indicated by the arrows to advance a paper web 26 over successive rolls, the web being alternately in contact with drying cylinders of the respective rows. An upper drier fabric 28 is supported above the web 26 by a plurality of guide rolls 30, 32, 34, 38, 40 42, 44.

The disposition of these guide rolls urges the upper drier fabric against the upper parts of the upper drying cylinders 10, 12, 14, 16 with the web 26 therebetween. This holds the web against the upper part of the respective drying cylinders. Similarly, a lower drier fabric 46 is supported below the web 26 by a plurality of guide rolls 48, 50, 52, 56, 58, 60, 62 and the lower drier fabric holds the web 26 against the lower parts of the lower drying cylinders 18, 20, 22, 24. As is shownin FIGURE 1, the upper drier fabric 28 is supported out of engagement with the 'web 26 while the web passes under the lower drier rolls 18, 20, 22, 24 and the lower drier fabric 46 is out of contact with the web 26 as the web passes the upper drier rolls 10, 12, 14, 16. This defines and confines a plurality of open ended upper pockets 64, 66, 68 each bounded by the upper drier fabric 28, the paper web 26 and a respective lower drying cylinder 18, 20, 22. Similarly defined lower pockets 70, 72, 74 are bounded by the lower drier fabric 46, the paper web 26 and a respective upper drying cylinder 12, 14, 16.

In the operation of the drier section, the upper drying cylinders 10, 12, 14, 16 and lower drying cylinders 18, 20, 22, 24 are steam heated. The wet web is heated by the drying cylinders to evaporate water therefrom. A certain amount of the evaporated moisture travels into the respective pockets 64, 66, 63, 70, 72, 74 partly because the web wraps farther around the respective drying cylinders than the upper and lower drier fabrics and also because there is continued evaporation from the web after it leaves actual contact with the drying cylinders. This moisture must be removed from the pockets if the drying is to continue. The moisture will, of course, naturally flow out of the open ends of the respective pockets as there is a certain amount of circulation of air inherent at the open ends and the moisture naturally diffuses to the drier regions outside the pockets, diffusing from the high moisture levels to lower moisture levels. This, for example, reduces the moisture preferentially at the ends and results in a paper product that is drier at its edges than in the center, thus leaving the paper too dry at the edges or too wet in the center. In the present invention, means is provided for adequately ventilating the pocket as desired across the width of the machine to produce more uniform drying. As shown in FIGURE 1, pocket ventilating means 76, 78, 80, 82, 84, 86 are provided to ventilate the respective pockets. Warm dry air is supplied to each pocket ventilating means by use of a blower 88 through a duct 90 (only one blower and one duct are illustrated).

The pocket ventilating means 82 is shown in greater detail in FIGURES 2 to 5. As shown in FIGURE 2, the pocket ventilating means 82 comprises a delivery duct or air spreader 92 which terminates in nozzles 94 and 95, and operates to deliver the flow of air from the round duct 90 to the nozzles 94 and 95. As illustrated, the nozzles 94, 95 define respective narrow, elongated orifices 96, 97 extending lengthwise of the pockets. The air spreader 92 is mounted on an appropriate bracket 98 in a fixed relationship to the guide roll 50 so that the guide roll 50 is disposed across the open upper end of the air spreader 92 and near the nozzles 94 and 95. Indeed, the guide roll 50 cooperates with the nozzles 94 and 95 to define the exit orifices 96, 97 from the air spreader 92. As used herein, the term nozzles includes the means defining the exit orifices even though not projecting from the body of the air spreader. Vanes 99 and 100 may be used to provide the appropriate distribution of the air at the nozzles 94,

95. End plates 104 partially close the ends of the nozzles 94 and 95 to confine the air from the orifices 96, 97 to flow against the drier fabrics as air jets 106, 108.

In operation the blower 88 provides a supply of warm, relatively dry air to the duct. in sufiicient volume to purge the moisture from the respective pockets. The air should be warm enough not to condense moisture from the air in the pocket. Room air from the papermaking plant is often suitable; other times it may be desirable to heat the air in a conventional manner. More particularly, in respect to the pocket ventilating means 82, the dry air supplied to the duct 90 is transmitted by the delivery duct or air spreader 92 to the respective nozzles 94 and which, as shown particularly in FIGURE 4, are disposed adjacent thee drier fabric 46 but spaced therefrom. The nozzles direct the air toward thedrier fabric 46 in the regions where the pocket is on the other side from the nozzles. The disposition of the vanes and nozzles provide the appropriate distribution of air suitable for uniform drying conditions. The nozzles are disposed generally opposite the center of the fabric and extend a substantial distance both ways from the center in the cross machine direction.

If the flow of air were confined to the center, the air in the center of the pocket would become too dry relative to the other regions of the pocket because the dry air would combine with moisture being evaporated from the web and thus become wetter. as it moved outward to and through the open ends of the pocket. It is therefore important that the flow into the pocket be distributed along the cross machine length of the pocket. Although the orifices 96, 97 may extendcompletely across the fabric, it is often preferable that the orifices not extend completely across the fabric as the edges of the paper are naturally somewhat drier than the central part, and the additional flow of dry air to the edges adds relatively little to the purging action.

The vanes 99 are disposed to direct the air somewhat laterally, giving the air jets 106, 108 a velocity component in the cross machine direction as shown in FIG- URE 2. This lateral component directs air in the direction of the open ends of the pocket and carries moisture away in the desired direction without requiring the development of a static head of pressure; preferably this lateral component is made progressively larger relative to the normal component for the parts of the jet more remote from the center of the fabric. This provides a more efficient and uniform flow of air and thus promotes more efficient and uniform purging of the pockets. The net result is not only to reduce the moisture content of the pocket but to provide a desired distribution of moisture in the pocket that produces a more uniform drying of the web and hence the desired more uniform condition in the finished paper.

As noted above, the drier fabric utilized in the present invention must be many times more air permeable than conventional drier felts. The drier fabric for this invention is made in the form of an open mesh having an air permeability preferably of the order. of ten times greater than that of conventional drier felts. Permeability may be expressed in units of perms where 1 perm is by definition times the percentage permeability. For example, if air under certain conditions passes through a one square foot section of fabric at a rate only 2 percent of the rate through a completely open square foot opening, the permeability of thefabric is 200 perms. Drier felts typically have an air; permeability of 0 to 70 perms. 1

According to the present invention, the drier fabric used should have an air permeability of more than about 200 perms and preferably 700 to 800 perms. The upper limit of permeability is determined by the need for providing adequate support for the web.

The orifices 96,. 97 are restricted in order to provide respective jets of air 106, 108 at relatively high velocity while furnishing the volume rate of air desirable for purging the pockets. The linear velocity of these jets 106, 108

is made sufiiciently great that the kinetic energy of the air in these jets drives the air through the open drier fabric while at the same time providing a region of reduced static pressure between the nozzles 94, 95 and the fabric 46. This static pressure should be near or below atmospheric pressure. Under such conditions, relatively little air escapes between the nozzles 94, 95 and the fabric 46 without passing through the fabric 46 into the pocket 70. Preferably, the air jets create subatmospheric static pressures that actually educe additional air from outside the air spreader 92 and carry it through the fabric as shown at 110 and 112. To this end the air permeability of the drier fabric must be greater than that which might create a back pressure upon impingement of the respective air jets 106, 198 sufiicient to force a substantial portion of the air from the air spreader 92 out through the spaces between the respective nozzles 94, 95 and the fabric 46 without passing through the fabric.

It has proven satisfactory to eject air into each pocket at a rate of the order of 250 cubic feet lineal foot of fabric width. At the same time, an average linear velocity of the jet air of the order of 50 feet per second has proven satisfactory.

As an example, in a papermaking machine operating at 1650 feet per minute to produce newsprint paper 150 inches wide, each of the blowers 88 is operated to furnish air to each of the pocket ventilating means at the rate of about 3000 cubic feet a minute. This air is obtained from the air in the papermaking plant and is relatively warm and dry. The cross section of each of the oriffices is rectangular and about inch by 96 inches, thereby producing at each orifice a pet of air at an average linear velocity of about 50 feet per second. The velocity is not uniform across the fabric but is controlled by the adjustment of the vanes 99, 100. The drier fabrics 46, 28 are Woven of fibers made of Dacron and nylon. The fabric is woven with about strands per inch in the machine direction, each of 1500 denier, and about 24 strands per inch in the cross machine direction each of 1800 denier. The guide vanes 99, 100 are preferably adjusted by trial and error to direct greater flow into the regions of highest moisture content in order to provide a relatively uniform moisture distribution in the sheet. As noted above, this condition is often that where the moisture content in the pocket is uniformly distributed; however, it includes a compensating distribution such as the distribution complementing the distribution in a preceding or following unventilated pocket.

Although certain preferred embodiments of the present invention have been described herein in detail, various modifications may be made therein without departing from the scope of the invention as set forth in the following claims. For example, although the nozzles have been shown and described as each defining a long slit, each orifice may comprise a plurality of perforations extending in the cross machine direction. Further, the nozzles may be constructed to define orifices independently of the guide rolls.

What is claimed is:

1. In connection with drying apparatus for drying a paper web in a papermaking machine wherein the paper web being dried is caused, to travel alternately over drying cylinders of each of two rows of drying cylinders with a drier fabric having an air permeability of more than about 200 perms urging the paper web against the drying cylinders of one of the rows, the drier fabric being supported out of contact with said paper web as it travels over the drying cylinders of the other of the rows to thereby define at least one pocket bounded by the drier fabric, the paper web and one of the drying cylinders of the other row, the drying cylinders evaporating moisture from the paper web into the pocket: the method of ventilating the pocket which comprises ejecting air from a nozzle disposed adjacent the drier fabric but spaced therefrom opposite the pocket, the air being ejected in per minute per jet form toward said drier fabric over a substantial portion of said fabric extending in the cross machine direction in both directions from the center of the fabric, the linear velocity of said jet air being sufficient that no substantial portion thereof flows out through the space between said nozzle and said fabric Without passing through said fabric, said air being ejected at a volume rate to sweep moisture from said pocket to substantially lower the humidity therein.

2. In connection with drying apparatus for drying a paper web in a papermaking machine wherein the paper web being dried is caused to travel alternately over drying cylinders of each of two rows of drying cylinders with an open-mesh drier fabric having an air permeability of more than about 200 perms urging the paper web against the drying cylinders of one of the rows, the drier fabric being supported out of contact with said paper Web as it travels over the drying cylinders of the other of the rows thereby to define at least one open-ended pocket bounded by the drier fabric, the paper web and one of the drying cylinders of the other row, the drying cylinders evaporating moisture from the paper web into the pocket: the method of ventilating the pocket which comprises ejecting air from a nozzle disposed adjacent the drier fabric but spaced therefrom opposite the pocket, the air being ejected in jet form against said drier fabric over a substantial portion of said fabric extending in the cross machine direction in both directions from the center of the fabric, the static pressure of said jet air being no greater than about atmospheric whereby no substantial portion thereof flows out through the space between said nozzle and said fabric Without passing through said fabric, said air being ejected at a volume rate to sweep moisture from said pocket to substantially lower the humidity therein.

3. In connection with drying apparatus for drying a paper web in a papermaking machine wherein the paper web being dried is caused to travel alternately over drying cylinders of each of two rows of drying cylinders with an open-mesh drier fabric having an air permeability of more than about 200 perms urging the paper web against the drying cylinders of one of the rows, the drier fabric being supported out of contact with said paper web as it travels over the drying cylinders of the other of the rows thereby to define at least one pocket extending in the cross machine direction, open at each end and bounded by the dried fabric, the paper web and one of the drying cylinders of the other row, the drying cylinders evaporating moisture from the paper web into the pocket: the method of ventilating the pocket which comprises ejecting air from a nozzle disposed adjacent the drier fabric but spaced therefrom opposite the pocket, the air being ejected in jet form against said drier fabric over a substantial portion of said fabric extending in the cross machine direction in both directions from the center of the fabric, said air jet being given a substantial outward component in the direction of said open ends, which component is progressively relatively larger for the parts of the jet more remote from the center of the fabric, the static pressure of said jet air being no greater than about atmospheric whereby no substantial portion thereof flows out through the space between said nozzle and said fabric without passing through said fabric, said air being ejected at a volume rate to sweep moisture from said pocket to substantially lower the humidity therein, said volume rate being distributed in the cross machine direction to produce a substantially uniform moisture content in web.

4. In connection with drying apparatus for drying a paper web in a papermaking machine wherein the paper web being dried is caused to travel alternately over drying cylinders of each of two rows of drying cylinders with drier fabric having an air permeability of more than about 200 perms urging the paper web against the drying cylinders of one of the rows, the drier fabric being supported out of contact with said paper web as it travels over the drying cylinders of the other of the rows thereby to define at least one pocket bounded by the drier fabric, the paper web and one of the drying cylinders of the other row, the drying cylinders evaporating moisture from the paper web into the pocket: the method of ventilating the pocket which comprises ejecting air at the rate of the order of 250 cubic feet per minute per lineal foot of fabric width from a nozzle disposed adjacent the drier fabric but spaced therefrom opposite the pocket, the air being ejected in jet form against said drier fabric over a substantial portion of said fabric extending in the cross machine direction in both directions from the center of the fabric, the average linear velocity of said jet air being of the order of 50 feet per second whereby no substantial portion thereof flows out through the space betwen said nozzle and said fabric without passing through said fabric.

5. Drying apparatus for drying a paper web in a papermaking machine comprising two. substantially parallel rows of drying cylinders over which the paper web to be dried may be caused to travel, alternating between a drying cylinder of one of said two rows and a drying cylinder of the other of said two rows; a drier fabric having an air permeability of more than about 200 perms urged against said drying cylinders of said one row for urging a paper web against said drying cylinders of said one row; means for supporting said dried fabric out of contact with said paper web as it travels over a drying cylinder of said other row thereby defining at least one pocket bounded by said drier fabric, said paper web and said drying cylinder of said other row, said pocket during operation receiving moisture evaporated from said paper web by the action of said drying cylinders; a delivery duct having an inlet end and terminating in a nozzle disposed adjacent said dried fabric but spaced therefrom opposite said pocket; and blower means for supplying relatively dry air to said inlet end of said duct, said nozzle extending in the cross machine direction a substantial distance both ways from the center of said fabric and having a cross section relative to the flow of air through said duct to produce a jet of air directed toward said drier fabric at sufficient linear velocity that no substantial portion thereof flows out through the space between said nozzle and said fabric without passing through said fabric.

6. Drying apparatus for drying a paper web in a papermaking machine comprising two substantially parallel rows of drying cylinders over which the paper web to be dried may be caused to travel, alternating between a drying cylinder of one of said two rows and a drying cylinder of the other of said two rows; a drier fabric having an air permeability of more than about 200 perms urged against said drying cylinders of said one row for urging a paper web against said drying cylinders of said one row; a guide roll for supporting said drier fabric out of contact with said paper Web as it travels over a drying cylinder of said other row thereby defining at least one pocket bounded by said drier fabric, said paper web and said drying cylinder of said other row, said pocket during operation receiving moisture evaporated from said paper web by the action of said drying cylinders; a delivery duct having an inlet end and terminating in a pair of nozzles disposed adjacent said drier fabric but spaced therefrom adjacent said guide roll; and blower means for supplying relatively dry air to said inlet end of said duct, said nozzles each extending in the cross machine direction a substantial distance both ways from the center of said fabric and with said guide roll defining an orifice having a cross section relative to the flow of air through said duct to produce a jet of air directed toward said drier fabric at sufficient linear velocity that no substantial portion thereof flows out through the space between said nozzle and said fabric without passing through said fabric.

7. Drying apparatus for drying a paper web in a papermaking machine comprising two substantially parallel,

rows of drying cylinders over which the paper web to be 8 dried may be caused to travel, alternating between a dry ing cylinder of one of said two rows and a drying cylinder of the other of said two rows; a drier fabric having an air permeability of more than about 200 perms urged against said drying cylinders of said one row for urging a aper web against said drying cylinders of said one row; means for supporting said drier fabric out of contact with said paper web as it travels over a drying cylinder of said other row thereby defining at least one pocket bounded by said drier fabric, said paper web and said drying cylinder of said other row, eration receiving moisture evaporated from said paper web by the action of said drying cylinders; a delivery, duct having an inlet end and terminating in a nozzle disposed adjacent said drier fabric but spaced therefrom opposite said pocket; and blower means for supplying relatively dry air to said inlet end of said duct, said nozzle providing restricted egress from said delivery duct extending in t the cross machine direction a substantial distance both ways from the center of said fabric and having a cross section restricted relative to the flow of air through. said duct to produce a jet of air directed toward said drier fabric at sufficient linear velocity that no substantial portion thereof flows out through the space between said nozzle and said fabric without passing through said fabric, the

volume of dry air per unit time supplied by said blower means being sufiicient to sweep-out a substantial portion of said moisture from said pocket to substantially lower the humidity therein.

8. Drying apparatus for drying a paper web in a papermaking machine comprising two substantially parallel rows of drying cylinders over which the paper web to be dried may be caused to travel, alternating between a drying cylinder and one of said two rows and a drying cylinder of the other of said two rows; an open-mesh, air permeable drier fabric urged against said drying cylinders of said one row for urging a paper web against said drying cylinders of said one row; means for supporting said drier fabric out of contact with said paper web as it travels over a drying cylinder of said other row thereby defining at least one pocket bounded by said drier fabric,

said paper web and said drying cylinder of said other row,

said pocket during operation receiving moisture evaporated from said paper web by the action of said drying cylinders; a delivery duct having an inlet end and terminating in a nozzle disposed adjacent said drier fabric but spaced therefrom opposite said pocket; and blower means for supplying relatively dry air to said inlet end of said duct, said nozzle providing egress from said delivery duct extending in the cross machine direction a substantial distance both ways from the center, of said fabric and having a cross section relative to the flow of air through said duct to produce a jet of air directed toward said drier fabric at static pressure no greater than about atmospheric, the air permeability of said drier fabric being so great that no substantial portion of said air flows out through the space between said nozzle and said fabric without passing through said fabric, the volume of dry air per unit time supplied by said blower means being sufficient to sweep out a substantial portion of said moisture from said pocket to substantially lower the humidity therein.

9. Drying apparatus for drying a paper web in a paper making machine comprising two substantially parallel rows of drying cylinders over which the paper web to be dried may be caused to travel, alternating between a drying cylinder of one of said two rows and a drying cylinder of the other of said two rowsya drier fabric having an air permeability of the order of 1700 perms urged'against said drying cylinders of said one row for urging a paper web against said drying cylindersof said one row; means for supporting said drier fabric out of contact with said paper web as it travels over a drying cylinder of said other row thereby defining at least one pocket bounded by said drier fabric, said paper web and said drying cylina said pocket during opder of said other row, said pocket during operation receiving moisture evaporated from said paper web by the action of said drying cylinders; a delivery duct having an inlet end and terminating in a nozzle disposed adjacent said drier fabric but spaced therefrom opposite said pocket; and blower means for supplying relatively dry air to said inlet end of said duct at a rate of the order of 3000 cubic feet per minute, said nozzle providing egress from said delivery duct extending in the cross machine direction a substantial distance both ways from the center of said fabric and having a cross section relative to the flow of air through said duct to produce a jet of air directed toward said drier fabric at an average linear velocity of the order of 50 feet per second whereby no substantial portion thereof flows out through the space between said nozzle and said fabric without passing through said fabric.

10. Drying apparatus for drying a paper web in a papermaking machine comprising two substantially parallel rows of drying cylinders over which the paper web to be dried may be caused to travel, alternating between a drying cylinder of one of said two rows and a drying cylinder of the other of said two rows; an open-mesh, air permeable drier fabric urged against said drying cylinders of said one row for urging a paper web against said drying cylinders of said one row; means for supporting said drier fabric out of contact with said paper web as it travels over a drying cylinder of said other row thereby defining at least one pocket bounded by said drier fabric, said paper web and said drying cylinder of said other row, said pocket during operation receiving moisture evaporated from said paper web by the action of said drying cylinders; a delivery duct having an inlet end and terminating in a nozzle disposed adjacent said drier fabric but spaced therefrom opposite said pocket; and blower means for supplying relatively dry air to said inlet end of said duct, said nozzle providing egress from said duct extending in the cross machine direction a substantial distance both ways from the center of said fabric and having a cross section relative to the flow of air through said duct to produce a jet of air directed toward said drier fabric, the air permeability of said drier fabric being greater than that which creates back pressure upon impingement of said jet sufiicient to force a substantial portion of said dry air out through the space between said nozzle and said fabric without passing through said fabric, the volume of dry air per unit time supplied by said blower means being suflicient to sweep out said moisture from said pocket to substantially lower the humidity therein.

11. Drying apparatus for drying a paper web in a papermaking machine comprising two substantially parallel rows of drying cylinders over which the paper web to be dried may be caused to travel, alternating between a drying cylinder of one of said two rows and a drying cylinder of the other of said two rows; an open-mesh, air permeable drier fabric urged against said drying cylinders of said one row for urging a paper web against said drying cylinders of said one row; means for supporting said drier fabric out of contact with said paper web as it travels over a drying cylinder of said other row thereby defining at least one pocket bounded by said drier fabric, said paper web and said drying cylinder of said other row, said pocket during operation receiving moisture evaporated from said paper web by the action of said drying cylinders; a delivery duct having an inlet end and terminating in a nozzle disposed adjacent said drier fabric but spaced therefrom opposite said pocket; and blower means for supplying relatively dry air to said inlet end of said duct, said nozzle providing egress from said duct to produce a jet of air directed toward said drier fabric, the air permeability of said drier fabric being greater than that which creates back pressure upon impingement of said jet suflicient to force a substantial portion of said dry air out through the space between said nozzle and said fabric without passing through said fabric, said nozzle extending in the cross machine direction a substantial distance both ways from the center of said fabric, said delivery duct including distribution means for directing the flow of air through said nozzle in the distribution across said fabric that produces a substantially uniform moisture content in said web.

12. Drying apparatus for drying a paper Web in a papermaking machine comprising two substantially parallel rows of drying cylinders over which the paper web to be dried may be caused to travel, alternating between a drying cylinder of one of said two rows and a drying cylinder of the other of said two rows; an open-mesh, air permeable dried fabric urged against said drying cylinders of said one row for urging a paper web against said drying cylinders of said one row; means for supporting said drier fabric out of contact with said paper web as it travels over a drying cylinder of said other row thereby defining at least one pocket bounded by said drier fabric, said paper web and said drying cylinder of said other row, said pocket during operation receiving moisture evaporated from said paper web by the action of said drying cylinders; a delivery duct having an inlet end and terminating in a nozzle disposed adjacent said drier fabric but spaced therefrom opposite said pocket; and blower means for supplying relatively dry air to said inlet end of said duct, said nozzle providing restricted egress from said duct to produce a jet of air directed toward said drier fabric, the air permeability of said drier fabric being greater than that which creates back pressure upon impingement of said jet sufficient to force a substantial portion of said dry air out through the space between said nozzle and said fabric without passing through said fabric, said nozzle extending in the cross machine direction a substantial distance both ways from the center of said fabric, said delivery duct including distribution means for directing the flow of air through said nozzle in the distribution across said fabric that produces a substantially uniform relatively lower moisture content in said pocket along substantially its entire length.

13. Drying apparatus for drying a paper Web in papermaking machine comprising two substantially parallel rows of drying cylinders over which the paper web to be dried may be caused to travel, alternating between a drying cylinder of one of said two rows and a drying cylinder of the other of said two rows; an air permeable drier fabric urged against said drying cylinders of said one row for urging a paper web against said drying cylinders of said one row; means for supporting said drier fabric out of contact with said paper web as it travels over a drying cylinder of said other row thereby defining at least one pocket bounded by said drier fabric, said paper web and said drying cylinder of said other row, said pocket extending in the cross machine direction and being open at each end, said pocket during operation receiving moisture evaporated from said paper web by the action of said drying cylinders; a delivery duct having an inlet end and terminating in a nozzle disposed adjacent said drier fabric but space-d therefrom opposite said pocket; and blower means for supplying relatively dry air to said inlet end of said duct, said nozzle providing egress from said duct to produce a jet of air directed toward said drier fabric at sufficient linear velocity that no substantial portion thereof flows out through the space between said nozzle and said fabric without passing through said fabric, said nozzle extending in the cross machine direction a substantial distance both ways from the center of said fabric, said delivery duct including distribution means for directing the flow of air through said nozzle in the distribution across said fabric that produces a substantially uniform moisture content in said web along substantially its entire width, said distribution means giving the motion of said jet from said nozzle a substantial outward component in the direction of said open ends, which component is pro- 11 12 gressively relatively larger for the parts of the jet more 3,250,019 5/1966 Beachler 34-1 17 3,263,344 8/1966 Stickle 34-116 remote from the center of said fabric.

FOREIGN PATENTS References Cited 14 660 6/1914 Gre tBrita'n UNITED STATES PATENTS a 1 1,199,394 9/1916 Liebeck 34-111 3,110,575 11/1963 Justus 34111 KENNETH W. SPRAGUE, Primary Examiner. 

1. IN CONNECTION WITH DRYING APPARATUS FOR DRYING A PAPER WEB IN A PAPERMAKING MACHINE WHEREIN THE PAPER WEB BEING DRIED IS CAUSED TO TRAVEL ALTERNATELY OVER DRYING CYLINDERS OF EACH OF TWO ROWS OF DRYING CYLINDERS WITH A DRIER FABRIC HAVING AN AIR PERMEABILITY OF MORE THAN ABOUT 200 PERMS URGING THE PAPER WEB AGAINST THE DRYING CYLINDERS OF ONE OF THE ROWS, THE DRIER FABRIC BEING SUPPORTED OUT OF CONTACT WITH SAID PAPER WEB AS IT TRAVELS OVER THE DRYING CYLINDERS OF THE OTHER OF THE ROWS TO THEREBY DEFINE AT LEAST ONE POCKET BOUNDED BY THE DRIER FABRIC, THE PAPER WEB AND ONE OF THE DRYING CYLINDERS OF THE OTHER ROW, THE DRYING CYLINDERS EVAPORATING MOISTURE FROM THE PAPER WEB INTO THE POCKET: THE METHOD OF VENTILATING THE POCKET WHICH COMPRISES EJECTING AIR FROM A NOZZLE DISPOSED ADAJACENT THE DRIER FABRIC BUT SPACED THEREFROM OPPOSITE THE POCKET, THE AIR BEING EJECTED IN JET FORM TOWARD SAID DRIER FABRIC OVER A SUBSTANTIAL PORTION OF SAID FABRIC EXTENDING IN THE CROSS MACHINE DIREC- 